During radio frequency (RF) processing, geometrical factors such as distance between electrodes and projection of top electrode on the samples' exposed surface area (area that electric field passes through the sample) have a certain effect on power absorption, temperature distribution, heating rates and heating uniformity in the samples. Knowing the role played by these factors can be helpful for further studies in optimization of design parameters of an RF heating process. Therefore, to evaluate effect due to distance between electrodes and projection area during RF heating process, samples of same volume but exhibiting different projection areas were used to determine the variability in their power absorption, temperature change and heating rates. RF electrodes in this system were positioned with a fixed gap between samples' top-bottom surfaces and the electrodes and, case by case, at different distance between electrodes. The results indicated that both parameters have strong effect on power absorption, temperature distribution, heating rates and heating uniformity in the samples, which is further amplified when it is combined with the change of dielectric properties with temperature. In the investigated range, wider projection area and shorter distance between electrodes led to faster heating, in terms of average temperature, but less uniform temperature distribution, at least in the early stage of the RF heating process, before the changes in dielectric properties of the heated load started modifying the trend of the loss tangent and penetration depth. The results of this study are expected to be used in planning geometrical configuration and design parameters of RF systems and sample dimensions for further optimization studies. © 2016 The Institution of Chemical Engineers.
Computer simulation of radio-frequency heating applied to block-shaped foods: Analysis on the role of geometrical parameters
MARRA, Francesco
2016-01-01
Abstract
During radio frequency (RF) processing, geometrical factors such as distance between electrodes and projection of top electrode on the samples' exposed surface area (area that electric field passes through the sample) have a certain effect on power absorption, temperature distribution, heating rates and heating uniformity in the samples. Knowing the role played by these factors can be helpful for further studies in optimization of design parameters of an RF heating process. Therefore, to evaluate effect due to distance between electrodes and projection area during RF heating process, samples of same volume but exhibiting different projection areas were used to determine the variability in their power absorption, temperature change and heating rates. RF electrodes in this system were positioned with a fixed gap between samples' top-bottom surfaces and the electrodes and, case by case, at different distance between electrodes. The results indicated that both parameters have strong effect on power absorption, temperature distribution, heating rates and heating uniformity in the samples, which is further amplified when it is combined with the change of dielectric properties with temperature. In the investigated range, wider projection area and shorter distance between electrodes led to faster heating, in terms of average temperature, but less uniform temperature distribution, at least in the early stage of the RF heating process, before the changes in dielectric properties of the heated load started modifying the trend of the loss tangent and penetration depth. The results of this study are expected to be used in planning geometrical configuration and design parameters of RF systems and sample dimensions for further optimization studies. © 2016 The Institution of Chemical Engineers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
